The present invention relates to performance improving additives for surfactant foaming solutions which are injected in conjunction with steam or carbon dioxide floods to improve conformance.
When an oil reservoir is subjected to steam injection, steam tends to move up in the formation, whereas condensate and oil tends to move down due to the density difference between the fluids. Gradually, a steam override condition develops, in which the injected steam sweeps the upper portion of the formation but leaves the lower portion untouched. Injected steam will tend to follow the path of least resistance from the injection well to a production well. Thus, areas of high permeability will receive more and more of the injected steam which further raises the permeability of such areas. This phenomenon exists to an even larger degree with low injection rates and thick formations. The steam override problem worsens at greater radial distances from the injection well because steam flux decreases with increasing steam zone radius.
Although residual oil saturation in the steam swept region can be as low as 10%, the average residual oil saturation in the formation remains much higher due to poor vertical conformance. Thus it is because of the creation of steam override zones that vertical conformance in steam floods is usually poor.
A similar conformance problem exists with carbon dioxide flooding. Carbon dioxide has a large tendency to channel through oil in place since carbon dioxide viscosity may be 10 to 50 times lower than the viscosity of the oil in place. This problem of channeling through oil is exacerbated by the inherent tendency of a highly mobile fluid such as carbon dioxide to preferentially flow through more permeable rock sections. These two factors, unfavorable mobility ratios between carbon dioxide and the oil in place and the tendency of carbon dioxide to take advantage of permeability variations, often make carbon dioxide flooding uneconomical. Conformance problems increase as the miscibility of the carbon dioxide with the oil in place decreases.
Although not much attention has been devoted to carbon dioxide conformance, it has long been the concern of the oil industry to improve the conformance of a steam flood by reducing the permeability of the steam swept zone by various means. The injection of numerous chemicals such as foams, foaming solutions, gelling solutions or plugging or precipitating solutions have been tried. Because of the danger of damaging the reservoir, it is considered important to have a non-permanent means of lowering permeability in the steam override zones. For this reason, certain plugging agents are deemed not acceptable. In order to successfully divert steam and improve vertical conformance, the injected chemical should be (1) stable at high steam temperatures of about 300.degree. to about 600.degree. F., (2) effective in reducing permeability in steam swept zones, (3) non-damaging to the oil reservoir and (4) economical.
The literature is replete with references to various foaming agents which are employed to lower permeability in steam swept zones. The foaming agents of the prior art require the injection of a non-condensable gas to generate the foam in conjunction with the injection of steam and the foaming agent. U.S. Pat. Nos. 3,366,175 and 3,376,924 disclose the injection of a steam foam in a hydrocarbon reservoir at the interface between the hydrocarbons and the gas cap to aid in recovery. U.S. Pat. Nos. 3,410,344 and 3,994,345 disclose the use of a steam foaming agent selected from the generic groups of polyethoxyalkanols and alkylaryl sulfonates to reduce permeability in steam channels. The use of similar surfactants such as sodium lauryl sulfoacetate and alkyl polyethylene oxide sulfate are disclosed as foaming agents in carbon dioxide foams in U.S. Pat. Nos. 4,088,190 and 4,113,011, respectively. U.S. Pat. No. 4,018,278 discloses the use of sulfonated, ethoxylated alcohols or alkylphenols in surfactant flooding solutions without the use of steam.
Several trademarked foaming agents have been field tested by petroleum companies in steam floods. These include such trademarked chemicals as "STEPANFLOW 30", an alpha olefin sulfonate--sold by Stepan Chemical Co., "SUNTECH IV", a sulfonate--sold by Sun Oil, "THERMOPHOAM BWD", an alpha olefin sulfonate--sold by Farbest Co., "COR-180", a sulfonate--sold by Chemical Oil Recovery Co., and "SD1020", an alkyl toluene sulfonate sold by Chevron Inc. U.S. Pat. No. 4,086,964 disclosed the use of lignin sulfonates for a foaming agent and U.S. Pat. No. 4,393,937 discloses the use of alpha olefin sulfonates as a steam foaming agent. See also United Kingdom Patent No. 2,095,309 for a disclosure of alpha olefin sulfonate foaming agents.
Disclosures of laboratory and field tests of Stepanflo are contained in SPE Paper No. 10774 entitled "The Laboratory Development and Field Testing of Steam/Noncondensable Gas Foams for Mobility Control in Heavy Oil Recovery" by Richard E. Dilgren et al. presented at the 1982 California Regional Meeting of the SPE held in San Francisco Mar. 25-26, 1982 and the Journal of Petroleum Technology, July, 1982, page 1535 et seq. The same Journal of Petroleum Technology also discusses tests conducted on "THERMOPHOAM BWD". Additional information on tests of "THERMOPHOAM BWD" are also disclosed in Department of Energy Publications DOE/SF-10761-1, -2 and -3.
Tests of the "COR-180" foaming agent of Chemical Oil Recovery Co. are disclosed in SPE Paper No. 11806 entitled "Improvement in Sweep Efficiencies in Thermal Oil-Recovery Projects through the Application of In-Situ Foams" by R. L. Eson, presented at the International Symposium on Oil Field and Geothermal Chemistry in Denver, Jun. 1-3, 1983 and Department of Energy Reports No.s DOE/SF/10762-1, -2, -3.
U.S. Pat. Nos. 4,540,049; 4,540,050; and 4,577,688 disclose the injection of a group of novel steam foaming agents for injection with steam to decrease permeability in steam swept zones. The steam foaming agents have the general formula: EQU RO(R'O).sub.n R"SO.sub.3 M
where R is an alkyl radical, branched or linear, or an alkylbenzene, alkyltoluene or alkylxylene group, having from about 8 to about 24 carbon atoms in the alkyl chain, R' is ethyl, propyl or a mixture of ethyl and propyl, n has an average value of about 1 to about 20, R" is ethyl, propyl, hydroxypropyl or butyl and M is an alkali metal or ammonium ion.
U.S. Pat. No. 5,027,898 discloses novel lignin phenol surfactant compounds for use as steam foaming or carbon dioxide foaming agents in hydrocarbon recovery.